Response variability is a fact of the brain. There can be dramatic differences in the responses of[unreadable] any given neuron, to any given stimulus, at different moments in time. Different neurons in any[unreadable] cortical area contributing to the representation of any given stimulus or action commonly have[unreadable] substantially different responses. Variations in distributed local, system, and brain-wide responses[unreadable] representing any given stimulus in any given behavioral context can differ radically in different[unreadable] individuals. At the same time, the brain operates with the maintenance of perceptual constancy,[unreadable] cognitive reliability, and learned-behavior stereotypy. How do we account for the robust behavioral[unreadable] representations of inputs and actions in the face of the marked response variability of their[unreadable] neurological representations? This project will address 3 issues. First, it will determine the basic[unreadable] consequences, for neurological response variability, of exposing neonatal rats across the critical[unreadable] period with stereotyped vs naturally variable complex acoustic (speech-like) stimulus sets. Second,[unreadable] it will determine whether or not and how systematically varying the modulatory inputs enabling[unreadable] learning-induced plasticity in adult brains contribute to distributed neuronal response variability and[unreadable] coordination, and to behavioral response variability, in an auditory stimulus recognition task. Third,[unreadable] it will investigate the relationships between variation in neuronal responses in the primary auditory[unreadable] cortex (A-1) and in "secondary" auditory cortical fields (PVAF; AAF; PAF;PPVAF), as a function of[unreadable] stimulus repertoire complexity, in trained adult rats. The long-term goal of this project is to[unreadable] determine how a neurological strategy of learning-driven abstraction and coordination can lead to[unreadable] new insights into how we can potentially revise learning strategies to improve their effectiveness[unreadable] and reliability for neuro-behaviorally impaired human populations.